1. Field of the Invention
The invention relates to cementitious binders and compositions made therefrom. In particular, the invention relates to binders comprising gypsum (calcium sulfate hemihydrate), Portland cement and silica fume, for use in cementitious compositions to made construction materials such as interior and exterior building materials, backer boards, fiberboard, floor underlayments, siding, trim boards, structural framing, floor and road patching materials, fire-proofing sprays, and fire-stopping materials.
2. Description of Related Technology
Construction materials, such as external siding and roofing, are typically not manufactured using a calcium sulfate hemihydrate component (i.e., partially dehydrated gypsum) because gypsum-containing materials usually have low water resistance. However, gypsum is a desirable component in construction materials due to its rapid cure and early strength characteristics. Attempts to improve the water-resistance of gypsum boards by mixing Portland cement and calcium sulfate hemihydrate have met with limited success because such a mixture can result in the formation of ettringite, which may cause expansion of the gypsum/Portland cement product and thus lead to its deterioration. It is believed that ettringite (3CaO.OMEGA.Al.sub.2 O.sub.3 .OMEGA.3CaSO.sub.4 .OMEGA.32H.sub.2 O) is formed when the alumina in the tricalcium aluminate (3CaO.OMEGA.Al.sub.2 O.sub.3) present in the Portland cement reacts with lime primarily from the dicalcium silicate (2CaO.OMEGA.SiO.sub.2) also present in the Portland cement, and the sulfate from the gypsum (CaSO.sub.4 .OMEGA.1/2H.sub.2 O), in the presence of water.
A cementitious composition useful as a pavement patching compound which contains Portland cement and alpha gypsum is disclosed in Harris, U.S. Pat. No. 4,494,990. The composition also includes a pozzolan source, such as, for example, silica fume, fly ash or blast furnace slag. The Harris patent discloses that the pozzolan blocks the interaction between the tricalcium aluminate and the sulfate from gypsum. The Harris patent discloses mixing a three-component blend of Type I Portland cement, alpha gypsum and a pozzolan source, silica fume, with a fine aggregate to prepare a mortar used to cast mortar cubes for evaluating the strength of the resulting composition. The Harris patent generally discloses a preference for pozzolans having a "high" degree of fineness, silica content, and degree of amorphousness of the silica.
Ortega et al., U.S. Pat. No. 4,661,159 discloses a floor underlayment composition that includes alpha gypsum, beta gypsum, fly ash and Portland cement. The patent also discloses that the floor underlayment material can be used with water and sand or other aggregate to produce a fluid mixture which may be applied to a substrate.
Sattler et al., U.S. Pat. No. 5,030,289 discloses a first group of molded construction parts made from waste paper or cellulose fibers and a binder made from (1) Portland cements, alumina cements, belite cements, or mixtures thereof; and (2) a pozzolan such as amorphous silicic acid, powdered trass, fly ash, or mixtures thereof. Sattler et al. also discloses a second group of molded construction parts made from fiber and a binder of (1) a latently hydraulic component such as blast sand or blast slag; (2) hemihydrate gypsum; and (3) Portland cement. However, the Sattler et al. patent does not disclose combining gypsum with the cement/pozzolan-containing mixtures used to make the first group of molded construction parts.